In an MOS transistor, a gate electrode is formed on an insulating layer between a source and drain region. A channel region is located between the source and drain region. A silicon oxide layer typically is used as the insulating layer between the gate electrode and the channel region.
Conventionally, the oxide layer is formed by oxidizing silicon under an O.sub.2 atmosphere. However, according to recent literature such as Hyunsang HWANG et al., Appl. Phys. Lett. Vol. 57. pp. 1010-1990 and Hyunsang HWANG et al., IEEE IEDM '90 p. 421, it is reported that, in the case of growing a gate oxide layer under an N.sub.2 O atmosphere, a certain amount of nitrogen may permeate into the Si/SiO.sub.2 interface. Thus, characteristics of the semiconductor device, such as a device including a MOSFET, may be improved. Boron also may penetrate into the gate oxide and the channel region in the case of using a P+ polysilicon gate electrode.
It could be said that the reliability of the semiconductor device improves by growing the gate oxide layer under an N.sub.2 O atmosphere, because the nitrogen partially eases the strain in the Si/SiO.sub.2 interface, so that generation of traps in the interface due to electrical stress possibly may be reduced.
By using an N.sub.2 O atmosphere instead of an O.sub.2 atmosphere in the oxidation process, the nitrogen simply may be included into the Si surface. However, since this reaction process needs a very high reaction temperature, in the case of utilizing a conventional process temperature, the thickness of the oxide layer formed becomes very thin and the nitrogen contained therein is relatively small in quantity.
According to a recent article, P. J. Tobin, Symp. on VLSI technology, 1993. P. 51, the N.sub.2 O is resolved into N.sub.2 of 64.3%, O.sub.2 of 31% and NO of 4.7% at a temperature of 950.degree. C. This article illustrates that the amount of nitrogen is directly related to that of NO. Thus, it is necessary that the amount of NO be increased so that the optimum nitrogen may penetrate more rapidly into the Si/SiO.sub.2 interface.
With known techniques, since resolution of N.sub.2 O occurs at a very high temperature, it takes a long time to react N.sub.2 O at a low temperature, and nitrogen obtained therefrom is of little quantity. If the value of the "temperature".times."time" becomes great, a junction forms deeply, and it is difficult for the resulting structure to be practically used in a new generation element. Since N.sub.2 reacts at the temperature of about 1050.degree. C., a reaction process should be carried out in a rapid thermal process. Thus, it is difficult to obtain a semiconductor device with good reliability and efficiency.